Flat panel display devices are increasingly gaining market acceptance for a variety of different applications. For example, active matrix liquid crystal displays (AMLCDs) have found widespread use as the video monitors in laptop computers, video cameras, and avionic navigation modules, to name a few. Other types of displays, such as electroluminescent (EL) and field emissive displays (FEDs) are also used in a variety of industrial and consumer applications. The advantage of each of these types of devices resides in the fact that they are all substantially flat, particularly as compared to the cathode ray tube that has been the standard for the past fifty years.
In the AMLCD, the elements which cause the desired optical characteristic are typically sandwiched between a pair of thin glass plates. These elements include first and second patterned electrodes for applying an electrical field to liquid crystal (LC) material disposed therebetween. Each pair of oppositely disposed patterned electrodes define a single picture element or pixel. The liquid crystal material disposed between the electrodes is typically of a single type, such as twisted nematic (TN), supertwist nematic (STN), chiral smectic and others. The applications of an electric field to the LC material causes it to change its orientation from a first condition to a second condition, for example from transparent to opaque. However, in order to control the orientation of the liquid crystals, it is necessary to provide numerous other optical elements, such as polarizers and alignment layers. A conventional AMLCD is described in, for example, U.S. Pat. Nos. 4,666,252; 4,715,685 and 5,061,040, all to Yaniv, et al, the disclosures of which are incorporated herein by reference.
Another type of display is the conventional passive liquid crystal display in which many of the additional layers and switching elements required for AMLCDs are not needed. For example, a standard passive display will typically include a layer of LC material disposed between the electrodes, which are themselves disposed on opposing substrates. While being much simpler to fabricate than AMLCDs and other display devices, they possess several limitations which have hindered uptake in the marketplace. For example, these devices, due to their relatively slow response time, are incapable of displaying information at video rates.
Another major limitation of the passive display is the difficulty associated with fabricating full color displays. Current technology requires the use of three discrete displays, one stacked atop the others, and each display dedicated to a particular color, e.g., red, green or blue. In order to accomplish this, it is necessary to use three different twisted nematic liquid crystal materials matched according to the formula: EQU d.alpha..epsilon.=n.lambda.
Where:
d=spacing between the discrete displays; PA1 .DELTA..epsilon.=is dielectric anisotropy PA1 n=is an integer PA1 .lambda.=wavelength of light (i.e., color) of the display.
This matching of displays is presently done by using different spacing (d) for each color, with the result being difficulty in manufacturing and low yield. Manufacturing problems and low yield are exacerbated by the need for spacers to be disposed in the displays to maintain proper spacing between the opposing display substrates. The chance for inappropriate spacing mounts as additional displays are mounted one atop another.
Other manufacturing problems commonly associated with conventional passive LCDs relate to uniform flow through of the LC material between the display substrates, and high likelihood of contaminating an entire display (rendering it useless) from the flow of but a single contaminant into the LC material. These problems are particularly acute in STN and smectic chiral display devices.
Accordingly there exists a need to provide a new type of display device that addresses the needs of the marketplace for a low cost reliable LCD device that is free from the problems inherent in the prior art Such a device should be relatively easy to manufacture, provide high manufacturing yields, demonstrate high reliability, be low cost, and take advantage of currently available manufacturing infrastructure. This device should also be able to provide full color, dynamic viewing angle, and present a low profile.